Add Snapcast TCP PCM sink and stream metadata
Register PCM_SINK_SNAPCAST_TCP and add a native pcm-tcp.c implementation
with FFI hooks (settings, sys bindings, discovery, UI and firmware
SOURCES).
Document FIFO vs TCP modes and mDNS auto-discovery. Note: TCP sink
reconnects on next play after errors and will drop the in-flight buffer
on
EPIPE; FIFO/stdout behavior is unchanged.
Add save_stream_metadata/update_stream_metadata and a playback metadata
override API so stream title/artist/album/length are surfaced
immediately.
Also add a netstream guard to clamp huge seeks that can hang streaming.